Manufacture of alternating electric current rectifiers



Patented Nov. 14, 1939 UNITED STATES PATENT OFFICE MANUFACTURE OF ALTERNATING ELEC- TRIO CURRENT RECTIFIERS No Drawing. Application February 4, 1938, Serial No. 188,813. In Great Britain February 18,

This invention relates to the manufacture of alternating electric current rectifiers of the dry surface contact type comprising. a body of metal having a compound of. the metal formed thereon and more particularly to rectifiers of the copper oxide type.

Rectifiers of this character as manufactured by the processes and under the conditions usually employed are liable to serious and hitherto inexplicable variations as regards their resistance in either or both directions of current flow and an abnormal creep or gradual decrease in resistance'in the reverse direction, the reverse creep being arever-sible phenomenon occurring during the application of a reverse voltage and not irreversible deterioration. In other respects also, such as defective adhesion of the cuprous oxide layer to the metal and irregularity in the thickness of the cuprous and cupric oxide, formed in the process of manufacture, a relatively large percentage of the rectifiers produced were from time to time so abnormal as to be unsuitable for service so that the production was seriously inefiicient.

It has now been discovered that the copper blanks from which the rectifier elements are produced by heat treatment in an oxidising atmosphere are extremely susceptible to contamination by certain impurities in this atmosphere of which sulphur, chlorine, bromine and iodine are definitely known to affect adversely the rectifier elements produced as regards the impor-- relatively low is arranged to be reduced or prevented.

This may be effected either by causing the blanks to be raised to the relatively high temperature as rapidly as possible or by preventing access of the contaminating atmosphere until the blanks have attained this temperature.

In carrying the invention into practice, the rate at which heat is supplied to the blanks in the oxidising furnace may be arranged to be increased until the blanks reach the final oxidising temperature as by initially raising the temperathe 2' cam. (01. 175-366) ture or by providing the furnace with sufiicient thermal capacity so that the introduction of the blanks into the furnace will not appreciably cool itand/or the surfaces of the blanks may be previously coated with a layer of a black material adapted to increase the rate of absorption of heat, such for example, as carbon, graphite'or cupric oxide.

Alternatively the blanks may be previously v coated with a layer of material adapted to protect the blanks from contact with the furnace 'the rate of absorption of heat must not itself contain any undesirable impurities which would cause contamination of the blanks as above described.

Having now particularly described and ascertained the nature of our said invention and in what manner the same is to be performed, we declare that what we claim is:

1. A process for the manufacture of alternating electric current rectifiers of the copper oxide type in'which the exposure of the rectifier blanks to the contaminating action of the oxidizing atmosphere during the period when the temperature of the blanks is low is arranged to be reduced or prevented by coating the blanks prior to heating them in the oxidizing atmosphere, with a layer of black material such as carbon, graphite or cupric oxide for the purpose of increasing the rate at which heat is absorbed by the blanks until the blanks reach the final oxldizing temperature.

2. A process for the manufacture of alternating electric current rectifiers of the copper oxide type in which the exposure of the rectifier blanks to the contaminating action of the oxidizing atmosphere during the period when the temperature of the blanks is low is arranged to be reduced or prevented by coating the blanks, prior to heating them in the oxidizing atmosphere,.

with a layer of protective material of such character as to be evaporated or burnt off when a relatively high temperature is obtained.

ALBERT LESLIE WILLIAMS. LESLIE ERNEST THOMPSON. ROGER HARRY ture of the furnace above the oxidising tempera- 

